Method and apparatus for ground radar information display system

ABSTRACT

Disclosed herein is a method and apparatus for a ground radar and information display system for commercial and general aviation. The method includes processing raw data from the presently existing ATCRBS system, duplicating the raw data and sending it to an auxiliary computer, filtering out non-positional messages of the raw data, encoding the raw data into a data block transmitting the data block to a display facility, where it is decoded and displayed. The apparatus of the invention includes and auxiliary ground computer and a smaller on-board computer for processing the data block.

FIELD OF THE INVENTION

This invention relates to radar surveillance and information gatheringand sending systems and more particularly to such systems which includean auxiliary computer for ground information gathering and an auxiliarycomputer for an on-board receiving unit.

BACKGROUND OF THE INVENTION

The subject of air traffic control and collision avoidance schemes hasdrawn much public and private concern. Currently, the U.S. Governmentthrough the Federal Aviation Administration (FAA) operates a nationwidesystem of ground stations which includes a search radar unit and a radarbeacon unit which jointly and independently feed a common digitizer withinformation about aircraft in the vicinity. This system is known as theair traffic control radar beacon system (ATCRBS).

The information gathered by ATCRBS is sent to a host computer via aseries of high speed modems. The host computer also known as the centralcomputer complex (CCC) or air traffic control center (ATCC) hostcomputer. The ATCC host computer then computes navigational and airtraffic information to the air traffic controllers' display terminal.The air traffic controller then relays this information to aircraft inthe immediate vicinity. More detailed information about the ATCRBS isfound in Stocker, U.S. Pat. No. 4,197,538, col. 1 11. 23-46 andSchneider, U.S. Pat. No. 4,161,729, col. 1, 11. 14-25 cited parts ofwhich are both incorporated herein by reference.

The search radar unit gathers information on all aircraft in thevicinity by sending out radio waves and keeping track of the reflectionsfrom same. Thus the search radar finds out whether an aircraft is in thevicinity and its azimuth and range. The radar beacon unit duplicates theazimuth and range information of the search radar and interrogates thetransponder on-board an aircraft obtaining the aircraft transponderidentification number as well as other information. This is standard FAAformat.

The information from both units is fed in parallel to the commondigitizer where it is placed in a form suitable for transmission to theATCC. Along with position information the common digitizer adds systemoverhead such as idle words to separate each interrogation.

The FAA is about to invoke rules which will make the TCAS-I and TCAS-II(Traffic Collision and Avoidance System) mandatory on all commoncarriers major airline carriers having more than 20 passengers. TheTCAS-II system is estimated to cost private airlines $200,000 for eachunit. Each on-board unit alone will cost approximately $100,000. Thepublic cost of TCAS-II is estimated at over $800 million.

Problems other than cost associated with the proposed TCAS-II are thatthe interrogation and reply channels of ATCRBS will become overloaded.The TCAS-II system goes through an "all-call" sequence to determinetransponder identification of all transponders in the vicinity. Aftergetting the transponder identification number, TCAS-II adds the numberto the role call and all identified Mode S transponders are locked outfuture "all call" sequences. However, Mode A and Mode C transponder cannot be locked out and will continue to respond to the "all call"sequence, adding to the system burden.

Additionally, aircraft without transponders will not be detected by thesystem. There are approximately 5,000 such general aviation aircraft. Inthe recent past these type of aircraft have been involved in asignificant number of near misses or actual collisions.

Finally, TCAS-II will be of limited range. This will make it exceedinglydifficult for the aircraft to make horizontal maneuvers. Greater rangeis needed to give pilots more to make such maneuvers.

Others have proposed less expensive alternatives to TCAS-II. Forexample, Crow in U.S. Pat. No. 4,454,510 proposes using a two-way datacommunication link between each of a plurality of controlled aircraftand the ATCC host computer. While this system is advantageous overTCAS-II because it does not add signals to the ATCRBS environment, itstill relays on the ATCC host computer, placing an unwanted burden onthe critical system. When traffic control is needed most will be whentraffic is the heaviest. This precisely when the ATCC host computer willbe taxed to its limit. That makes any further load placed on the ATCCcritical which could cause even Crow to fail when it will be needed themost.

Baldwin in U.S. Pat. No. 4,293,857 proposes an aircraft avoidance systemwhich allows aircraft to communicate directly with one another. Thissystem will require the expensive Mode S transponders to be aboard eachaircraft. In addition, Baldwin requires each aircraft to havingrelatively large computers on-board to do the required calculations andto do them fast enough to make the system work. This will meansubstantially increased expenses for each aircraft as well as additionalweight. Both weight and expense are mentioned as problems in Crow.

Schneider in U.S. Pat. No. 4,161,729 proposes the addition of indicatorcontrol panel and a separate receiver and decoder between thetransponder and the antenna of the aircraft. Again this means theaddition of a substantial expense to each aircraft and the ability toreceive only information from participating aircraft.

Stocker in U.S. Pat. No. 4,197,538 discloses a de-centralized systemwhere aircraft communicate directly with one another via a separateon-board FM broadcast and receiving station. Raw data from the commondigitizer is broadcast to each of the participating aircraft. Eachparticipating aircraft must then encode the data for display on theparticipating aircraft's screen. Stocker thus requires expensiveadditional on-board equipment as well as placing the additionalrequirement of the ATCC host computer to transmit to the participatingaircraft.

Meilander in U.S. Pat. No. 3,668,403 discloses a complex method andalgorithm for vehicle traffic control.

Although many have attempted to solve the long felt need discussed inthe above references, problems of complexity, high cost and completedata communication remain. What is needed is an aircraft traffic controlsystem that will work well with the existing ATCRBS as well as withfuture systems. This system should supplement and not place anyadditional burden on the ATCC host computer. In fact, the preferredsystem will be invisible to the ATCC host computer. The preferred systemshould supply even general aviation with complete data on other aircraftin the vicinity.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an apparatus and method fora ground radar and information display system which is compatible withthe presently existing ATCRBS components.

It is a further object of this invention to provide a ground radar andinformation display system which provides information to allparticipating GRIDS aircraft for avoiding collisions and to assist inperforming accurate navigational functions.

It is a further object of this invention to provide such a GRIDS networkto small airlines and general aviation.

In accordance with the above objects and those that will be mentionedand will become apparent below, the method of the ground radar andinformation display system in accordance with this invention includes:

acquiring data from the common digitizer of the presently existingATCRBS without affecting the transmission of the data to the ATCC hostcomputer, wherein azimuth and range information is acquired for allaircraft being tracked by the ATCRBS;

creating a plot message by filtering out non-positional data from thecommon database;

converting polar coordinates of the plot message to rectangularcoordinates;

creating and encoding a data block from the plot message containing dataon all aircraft being tracked by the ATC facility by using an auxiliarycomputer means;

reading the data block into temporary storage;

transmitting the data block to receiving stations;

receiving the data block at a receiving station;

decoding the data block; and

displaying the data in human readable form.

The preferred method of the invention includes the step of repeating theprocess over and over again to gain updated information on the display.The preferred method also includes storing the plot message inalternating files of RAM, assigning a time signature to the plotmessages and then reading the files alternatively into a data computerbased on the time signatures. Thus a continuous stream of data is fedinto the data computer.

To facilitate the method of the invention, an apparatus which forpresently existing Air Traffic Control facilities (ATC) which includes asearch radar unit, a radar beacon unit and a common digitizer isprovided which comprises:

an auxiliary portion of the ground facility, including;

means for acquiring data from the common digitizer;

means for filtering out non-positional data from the common digitizerand temporarily storing the positional data;

auxiliary ground computer means for performing data conversion andencoding on the positional data and temporarily storing the converteddata in a block; and

radio means for transmitting the encoded data block; and

a display facility, including;

means for receiving the encoded data block;

computer means for decoding the signal; and display means for displayinginformation from the ground station, whereby information from the groundstation can be displayed and updated at the receiving unit withoutaffecting any of the presently existing facilities.

The preferred apparatus in accordance with the invention includes a 32bit microprocessor and a 32 bit channel. This insures expeditioushandling of the data. The preferred apparatus further includes datastream splitter which is optically connected to the common digitizer.This insures that no matter what occurs with the auxiliary portion ofthe ground apparatus that the original data stream will proceedunaffected.

It is an advantage of this invention to provide all aircraft includinggeneral aviation with an affordable means of obtaining information andnavigational data on aircraft in the vicinity.

It is an additional advantage of this invention to provide a GRIDSnetwork which is compatible and invisible to the presently existing andfuture ATCRBS.

Further objects and advantages of this invention will become obviouswith reference to the detailed description of the invention below,wherein:

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of the ground facility of theapparatus of the ground radar and information display system (GRIDS) inaccordance with this invention.

FIG. 2 is a schematic representation of the on-board components of theapparatus of the ground radar and information display system inaccordance with this invention.

FIG. 3 is a flow chart of the data filter and buffer unit of GRIDS.

FIG. 4 is a flow chart of the data conversion computer of GRIDS.

FIG. 5 illustrates the format of the data block.

FIG. 6 illustrates the format of the radar track message.

FIG. 7 illustrates the format of a Mode A transponder track message.

FIG. 8 illustrates the format of a Mode C transponder track message.

FIG. 9 illustrates the format of a Mode S transponder track message.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described with reference to the drawingwherein like reference characters designate like or corresponding partsthroughout the several views. Referring particularly to FIG. 1, there isshown the ground portion of the ground radar information display system(GRIDS) in accordance with this invention, generally denoted by thenumeral 10.

The ground portion 10 includes the presently existing portion of the ATCcenter (ATCRBS) and an auxiliary portion of the ground facility inaccordance with this invention. The presently existing portion of theATC center includes an information gathering function comprising asearch radar unit 12 and the beacon radar unit 14. The search radar unit12 gathers information by sending out a radar signal and keeping trackof the reflections. It will be noted that the aircraft reflecting thesearch radar signal need not have any special instruments or any type oftransponder for information to be gathered. The information gathered bythe search radar unit is the fact that an aircraft is in the vicinity,its range and azimuth from the transmission point. Upon successivesweeps of the search radar unit 14, the bearing vector can bedetermined.

The beacon radar unit 14 interrogates each of the aircraft in thevicinity through their on-board transponder. Of course, if the aircrafthas no transponder, then no response will be forthcoming. There arepresently two types of transponders in wide spread use, Mode A and ModeC. The Mode A is an older type of transponder which replies with itstransponder identification number but without any information concerningits altitude. The Mode C transponder will reply to the beacon radar unit14 interrogatories with its encoded altitude as well as its transponderidentification number. The transponder identification number is alsoknown as the "4096" number. This number is changed according to the airtraffic controller at time of take-off by changing a setting eitherelectronically or by manual dials on the side of the transponder.

Another type of transponder is the Mode S transponder which is currentlyabout to be implemented by the FAA. The Mode S transponder replies tothe beacon radar unit 14 only when discreetly addressed. This means thatthe beacon radar unit 14 must know the aircraft's transponderidentification number and address the transponder accordingly before itwill respond. This varies from the Mode A or C transponder in that theymay be addressed by an "all-calls" interrogation simultaneously. TheMode S transponder responds to the beacon radar unit 14 with the sameinformation as the Mode C transponder.

The information from the search radar unit 12 and the beacon radar unit14 is fed in parallel to a common digitizer 16 through lines 18 and 20,respectively. The common digitizer 16 is a subsystem of the presentlyexisting ATCRBS, which converts the encoded analog responses from thesearch radar unit 14 and beacon radar unit 14 into a digital output. Thedigitized information is then sent to an ATCC host computer through abuffer and modem unit in the presently existing ATCRBS.

In the GRIDS system of the invention, the digitized information known asthe raw data string is sent to a data stream splitter 22 over line 24.The signal containing the raw data string is duplicated with theoriginal signal continuing over line 26 to the buffer and modem 28 ofthe presently existing ATCRBS. As described above, the informationcontinues to the ATCC host computer. Preferably the data stream splitter22 is coupled to the ATCC host computer by an optical coupler. Using theoptical coupler, even if there was rare feed back by the auxiliaryground components of GRIDS, no harm would come to the presently existingATCC system.

The duplicated signal containing the raw data string is then fed intothe data filter and buffer 30 over line 32. As will be described morefully with respect to FIG. 3, the data filter and buffer 30 filters theraw data string to eliminate all non-positional data messages. Thus, thesystem overhead which includes idle words as well as real time qualitycontrol is taken out of the raw data string. After filtering out thenon-positional messages, a plot message is created. The plot message isstored temporarily in the buffer portion of the data filter and buffer30 and subsequently read into a data conversion computer 34 over line36.

In the preferred embodiment, the data filter and buffer 30 has a firstset of RAM and a second of RAM. The data filter and buffer 30 creates afirst file, File 1 in the first set of RAM and a second file, File 2 inthe second set of RAM. After the raw data string is filtered a timesignature is added to create the plot message. The time signature isequal to the actual present time less the time when the raw data wasfirst acquired by ATCRBS. The raw data is processed and stored in File 1until a predetermined time limit is reached. Typically, this time limitwill be less than one full sweep of the radar. The data filter andbuffer 30 continues to process the raw data but now stores it in File 2.Upon the data conversion computer's 34 instruction File 1 and File 2 areread into the computer 34.

As will be described more fully with reference to FIG. 4, the dataconversion computer 34 converts the polar coordinates of the plotmessage into equivalent rectangular coordinates. The data conversioncomputer 34 also creates a data block 41 by encoding the plot messagewith updated and extrapolated data. A more detailed description of theblock of data is set forth below with reference to FIG. 5.

The encoded block of data is then sent to data buffer 38 over line 40.The data block 41 is temporarily stored in data buffer 38 until it issent to a radio transmitter 42 over line 44. The data conversioncomputer 34 controls the temporary storage of the data block 41. Thedata conversion computer 34 is preferably a 32 bit micro-computer havinga 32 bit bus. The 32 bit micro-computer preferably contains a 32 bitmicroprocessor for example Intel Corporation's 80386 or Motorola's 680XXfamily of processors are sufficient.

The radio transmitter 42 is preferably an FM transmitter and the signalis then modulated and sent out to receiving stations over an antenna 46as illustrated in schematic by transmission waves 48. The data block 41in sent in bursts so that a complete data block 41 is sent with eachburst. The preferred transmission rate is 100 K Baud to insure thatmultiple complete blocks of data are transmitted during each sweep ofthe ATCRBS.

Thus, the auxiliary portion of the ground facility in accordance withthis invention is invisible to the presently existing ATCRBS. Theauxiliary portion of the ground facility is inexpensive. It is estimatedthat the total cost of all the new components of the preferredembodiment is $20,000.

The display facility of the invention, generally denoted by the numeral50 will now be described with reference to FIG. 2. A radio receiver 52receives the transmission waves 48 from the ground facility through anantenna 54. The radio receiver 52 matches the transmitter 42. Thus inthe preferred embodiment the radio receiver 52 is an FM receiver havinga demodulator. After receipt, the data block 41 is sent to the on-boarddata buffer 56 over line 58. Upon a control signal from an on-boardcomputer 60, the data block 41 in temporary storage in on-board databuffer 56 is read into computer 60 over line 62.

The radio transmitter 42 is preferably multi-channeled. Thustransmissions of radio transmitter 42 do not interfere with adjacenttransmitters since they can be tuned to a different channel. Forexample, in the preferred embodiment, the transmitter 42 has 20 channelswhich can be received by the receiver 52. The preferred receiver 52 issimilarly equipped. The on-board computer 60 is directly connected tothe receiver in the preferred embodiment by control line 64. Theon-board computer 60 controls to which of the 20 channels the receiveris tuned and is capable of scanning the entire band width until thetransmitting signal is found.

The on-board computer 60 decodes the data block 41 into a form which issuitable for display on a video display terminal 66 by transmission ofthe decoded signal over line 68. With the addition of an on-boardoptical disk data storage unit 70 which communicates with on-boardcomputer 60 over line 72, many more advantages of the invention may berealized. For example, navigational information such as maps of aterminal facility, routes, and standard and instrument departureprocedures can be easily stored on the optical disks. At appropriatetime the desired disk is inserted in the on-board optical disk datastorage unit 70. The information is fed into on-board computer 60 andthe decoded block of data may be superimposed on the map or route ordesired information at the video display terminal 66. The program fordecoding the data block 41 is illustrated in Appendix A.

The preferred embodiment of the invention includes a Mode S transponderwhich can provide data links with other Mode S equipped aircraft. Anaudio warning speaker 71 is connected to the on-board computer 60 overline 72 to alert the flight of such warnings. All TCAS-II aircraft willbe required to have the Mode S transponder if the currently proposedfinal regulations of the FAA are adopted. This will apply equally toTCAS-III systems as well. Thus the invention is presently compatiblewith the existing ATCRBS and the future proposed systems as well.

Manual controls 74 are provided for tuning a transponder 76 to thecorrect 4096 number. In the preferred operation, the on-board computer60 automatically sets the transponder 76 4096 number. However, manualcontrols may override the number and serve other functions such as anacknowledgement of alert messages. The manual controls are alsoconnected to the on-board computer 60 over line 78 to promote ease ofoperation.

The transponder 76 is connected to the on-board computer 60 over atwo-way communication line 80. The two-way communication line serves toconnect on-board computer to Mode S data link. The display facility ofthe invention 50 may be installed on aircraft having either Mode A, ModeC or Mode S transponders. Of course certain advantages of GRIDS are notpresent if a Mode A or Mode C transponder is selected. For example,without a Mode S transponder the audio warning would not be communicatedto the aircraft. If the aircraft contains a Mode A transponder the datablock 41 will be different as will be described in more detail withrespect to FIGS. 7-9.

In the preferred embodiment, the on-board computer 60 collects theinformation from the instruments of the aircraft (not shown) andutilizes that information to establish a match with a track in the datablock.

The detailed operation of the data filter and buffer 30 will now bedescribed with reference to the flow chart 90 of FIG. 3. The raw data isencoded by the common digitizer 16 in a series of words and then readinto the data stream splitter 22. After duplication, the duplicatedsignal is sent to the data filter and buffer 30 where the raw datastring from the common digitizer 16 is filtered and written into thebuffer portion of data filter and buffer 30 as shown by block 98.

The encoding is an FAA standard format. Each message is separated by atleast one idle word. And each data message is always preceded by atleast one idle word. Each encoded word is read as illustrated by a block92. Idle words have an even parity and are the only encoded words tohave such a parity, so they are easily detectable.

The first decisional phrase of a decision block 94 requires each word tobe read until the present word is not an idle word. When the first dataword appears it will according to FAA standard format be preceded by anidle word. The second decisional phrase of decision block 94 requirespresent word to be preceded by an idle word. Thus the first word of eachdata message will be sent to the next decisional block 96.

In FAA standard format the first word of a data message indicateswhether the message is position, weather or part of system overhead. Thedata filter and buffer 30 then asks whether the message is of the typeto be passed. If the pass identifying word is not in the message, thenext word is read. If pass identifying word is in the message theremaining message is read as illustrated by block 98. It will be notedthat the message is read according to the same format above.

The message is read if it is in the middle because when the middle of amessage is reached when the present word is a data word and will havebeen preceded by another data word. Thus reading continues because theprevious word was not an idle work as required by the second part of thedecision block. The reading of the message is stopped only when a dataword is preceded by an idle word. Thus, reading the message stops whenthe first word of the next message is reached.

A clock 100 assigns a time signature to each message when the message iswritten to the buffer portion of data filter and buffer 30. This allowsGRIDS to keep track of the time for each data message as describedearlier.

The data conversion computer 34 will now be described in detail withreference to FIG. 4. As illustrated by block 102, the filtered data isread from the data filter and buffer 30 and the buffer is cleared. Thefirst unread message is read from RAM (either File 1 or File 2)depending on which was read last. The new data is calculated and addedto previously calculated fields as illustrated by block 104.

If the message matches an existing track, each aircraft in the vicinityon the ATCRBS has its own track, then the message and the calculated isentered and into a matching track array as illustrated by decisionalblock 106 and block 107. The track array is initialized when the dataconversion computer 34 is powered up. As illustrated by decisional block106 and block 108, if the message does not match an existing track, themessage is entered on an empty track array.

After entering the unread message, the data filter and buffer 30 asks ifall of the messages from either File 1 of File 2 have been read, asillustrated by a decisional block 110. If not all the messages have beenread from the file, the reading continues until the file is empty. Notethat as a new aircraft approaches the facility, the tracking array willbe opened with the first message, however, subsequent messages will formpart of an established tracking array.

When the file is empty the inactive tracks are cleared, as illustratedby block 112. Thus if an aircraft leaves the ATCRBS vicinity it will nolonger be carried by the auxiliary computer system in accordance withinvention.

Extrapolation is then performed by the data conversion computer 34 usingthe unread data from the file, as illustrated by block 114. A best fitline estimates position and vector for all tracks is then performed bythe data conversion computer 34. This information then defines the datablock 41. The data block 41 contains complete information on allaircraft being tracked by the ATCRBS.

The data block 41 is then read into the data buffer 38 for transmissionas described earlier, as illustrated by block 116. The next file is readand the unread data processed as described above. In this way the databeing display by the video display terminal 66 is constantly updated.

As illustrated by FIG. 5, a data block 41 comprises the radar site I/Das a 16 bit word, the number of radar tracks as a 16 bit word, thenumber of Mode A transponder tracks as a 16 bit word, the number of ModeC transponder tracks as a 16 bit word and the number of Mode Stransponder tracks as a 16 bit word, which are self explanatory. Thedata block 41 additionally comprises the radar track message which isthe information on all aircraft not carrying a transponder of any typeas a 60 bit word, the information on all aircraft carrying a Mode Atransponder as a 72 bit word, the information on all aircraft carrying aMode C transponder as a 96 bit word and the information on all aircraftcarrying a Mode S transponder as a 120 bit word.

The data block 41 of the preferred embodiment also includes weatherinformation including the weather map region number as an 8 bit word andweather picture for the region. The maximum allowable bits for theweather picture are 32,768. It is not anticipated that the completeweather picture will be either transmitted or displayed on a singlepass. Rather the information will be transmitted and displayed over thecourse of the transmission of several data blocks 41.

The program for creating the data block 41 is illustrated in Appendix B.

With respect to FIGS. 6-9, there is illustrated the format and contentof the radar track message 43, the Mode A transponder track message 73,the Mode C transponder track message 82 and the Mode S track message 84,respectively. As will be appreciated more extensive track information isgathered from Mode C and Mode S transponder than from either the radartrack message or the Mode A track message.

IN USE

It will be appreciated that GRIDS as set forth in this disclosure wouldwork in an acceptable manner if just one ground facility were inexistence with just one aircraft having the on-board display systemrecited above. However, it will be appreciated that other features ofGRIDS as set forth above are possible if many and preferably all of thepresent ATCRBS sites were equipped with GRIDS. For example, if the morethan 200 ATCRBS sites were each installed with GRIDS a fail safe networkwould occur. If one or even several of the ATCRBS sites were to losetheir ATCC host computer the GRIDS network would continue to work. Forexample, if the aircraft were in the vicinity of Site 1 and it failed,then the aircraft would use GRIDS to get position and vector informationall aircraft in the vicinity by using a combination of the closestavailable and working ATCRBS sites. This promotes safety in the eventthat TCAS-II is eventually adopted and is overloaded despite argumentsto the contrary. GRIDS would continue to work in a TCAS-II environmentsince it does not rely on the ATCC host computer and it is compatiblewith Mode S transponders, although not dependent on same.

A 4096 number setting of 1200 (base 8) is now used by aircraft notoperating under ATCC control. Numbers in the range of 1201 (base 8) to1277 (base 8) can be used by GRIDS equipped aircraft that are not underATCC control. The on-board GRIDS computer 60 can then adjust the 4096number within this range to find a discreet number to aid in selfidentification of a track in the data block 41.

While the foregoing detailed description has described severalembodiments of the ground radar and information display system inaccordance with this invention (GRIDS), it is to be understood that theabove description is illustrative only and not limiting of the disclosedinvention. Particularly, any type of auxiliary computer may be used forexample a work station or even an 8 bit microcomputer is within thescope of this invention. Thus the invention is to be limited only by theclaims as set forth below.

    __________________________________________________________________________    APPENDIX A                                                                    __________________________________________________________________________    00010 REM                                                                     00020 REM QUIKPLOT 11/5/87D                                                   00030 REM RADAR DATA SYSTEMS                                                  00040 REM BY SHULENBERGER                                                     00050 REM                                                                     00060 DIM NS!(8), EW!(8), ALT!(8), SPEED!(8), CLIMB!(8)                       00070 OPEN "I",1,"TRACK 790" REM REF. AIRCRAFT (NORTH BOUND)                  00080 OPEN "I",2,"TRACK 698"                                                  00090 OPEN "I",3,"TRACK 6EA"                                                  00100 OPEN "I",4,"TRACK 960"                                                  00110 OPEN "I",5,"TRACK 6AE"                                                  00120 OPEN "I",6,"TRACK 6EI"                                                  00130 OPEN "I",7,"TRACK 604"                                                  00140 OPEN "I",8,"TRACK 691"                                                  00150 WINDOW #1,,(0,0)-(512,384)                                              00160 WINDOW OUTPUT #1                                                        00170 COORDINATE WINDOW                                                       00180 CIRCLE 256,256,30 REM 3 NM CIRCLE                                       00190 CIRCLE 256,256,50 REM 5 NM CIRCLE                                       00200 CIRCLE 256,256,100 REM 10 NM CIRCLE                                     00210 CIRCLE 256,256,200 REM 20 NM CIRCLE                                     00220 PLOT 103,0 T0 404,512                                                   00230 PLOT 404,0 TO 103,512                                                   00240 PLOT 0,108 TO 512,404                                                   00250 PLOT 0,404 TO 512,108                                                   00260 PLOT 0,256 TO 512,256                                                   00270 PLOT 256,0 TO 256,512                                                   00280 FOR C = 1 TO 24                                                         00290 READ# 1, NSREF!, EWREF!, TRACKREF!, ALTREF!, SPEEDREF!, CLIMBREF!       00300 FOR B = 2 TO 8                                                          00310 READ# B, NS!(B), EW!(B), TRACK !(B), SPEED!(B), ALT!(B), CLIMB!(B)      00320 NEXT B                                                                  00330 FOR B = 2 TO 8                                                          00340 XPT = ((EW!(B)-EWREF!) * 10.0) + 256.0 REM 10 PIXELS/NM                 00350 YPT = ((NS!(B)-NSREF!) * -10.0) + 256.0 REM OR 10 NM/CIRCLE             00360 CIRCLE FILL XPT,YPT,2                                                   00370 NEXT B                                                                  00380 DELAY 10000                                                             00390 COLOR 0                                                                 00400 FOR B = 2 TO 8                                                          00410 XPT = ((EW!(B)-EWREF!) * 10.0) + 256.0                                  00420 YPT = ((NS!(B)-NSREF!) * -10.0) +]256.0                                 00430 CIRCLE FILL XPT.YPT.1                                                   00440 NEXT B                                                                  00450 COLOR-1                                                                 00460 NEXT C                                                                  00470 CLOSE                                                                   00480 END                                                                     __________________________________________________________________________

    __________________________________________________________________________    APPENDIX B                                                                    __________________________________________________________________________    00010 REM                                                                     00020 REM TRACK WRITER 11/4/87                                                00030 REM RADAR DATA SYSTEMS                                                  00040 REM                                                                     00050 DIM A(10),TIME!(50)M,EW!(50)                                            00060 TIME! = 0                                                               00070 ALT! = 0                                                                00080 NS! = 0                                                                 00090 EW! = 0                                                                 00100 P!! = ATN(1)<<2                                                         00110 OPEN "I",#1,"FILTER1"                                                   00120 OPEN"0",#2,"TRACK 698"                                                  00130 CODE$ = 0698                                                            00140 ADAPTER1$ = "F1C5"                                                      00150 ADAOTER2$ = "C2C5"                                                      00160 NUMSEC = 300                                                            00170 L = 1                                                                   00180 FOR P = 1 TO 10                                                         00190 READ#1,A(P)                                                             00200 NEXT P                                                                  00210 TZERO! = A(10)/10.0                                                     00220 DO                                                                      00230 IF INKEY$ = "S" THEN GOTO 310                                           00240 FOR P = 1 TO 10                                                         00250 READ#1,A(P)                                                             00260 NEXT P                                                                  00270 IF (A(10)/10.0) > (TZERO! ⃡ 300.0) THEN GOTO 310            00280 IF HEX$(A(4)) = CODE$ THEN GOSUB "WRITE LINE"                           00290 TIMENOW! A(10)/10.0                                                     00300 UNTIL TIMENOW! - TZERO! ≧ NUMSEC                                 00310 CLOSE                                                                   00320 END                                                                     00330 "WRITE LINE"                                                            00340 RANGE! = (A(2)>>1)/8.0                                                  00350 AZIMUTH! = (A(3)*360.0)/4096.0                                          00360 TIME!(L) = (1(10)/10.0) - TZERO!                                        00370 DTIME! = TIME!(L) - TIME!(L - 1)                                        00380 ALT!(L) = A(7) MOD 4096/10.0                                            00390 NS!(L) = RANGE! * COS((p!!*AZIMUTH!)/180.0)                             00400 EW!(L) = RANGE' * SIN((P!!*AZIMUTH!)/180.0)                             00410 VEL! = 3600.0 * ((SOA((NS!(L)-NS!(L-1))2 + (EW!(L) - EW!(L - 1))        2))/DTIME!)                                                                   0420 CLIMB! = 60000.0 * ((ALT!(L)-ALT!(L-1)/DTIME!)                           00430 IF L = 1 GOTO 460                                                       00440 GOSUB "CALCULATE HEADING"                                               00450 WRITE*1NS!(L), EW!(L), HEADING!, VEL!, ALT!(L), CLIMB!                  00460 L = L + 1                                                               00470 RETURN                                                                  00480 "CALCULATE HEADING"                                                     00490 DELTA X! = NS!(L) - NS!(L-1)                                            00500 DELTA Y! = EW!(L-1) - EW!(L)                                            00510 RAWARC! = ATN (DELTA Y!/DELTA X!)                                       00520 PINUM = 0                                                               00530 IF DELTA X! < 0:0 THEN PINUM = 1                                        00540 IF DELTA X! > 0.0 AND DELTA Y! < 0.0 THEN PINUM = 2                     00550 TRUEARC! = RAWARC! + (PINUM * P!!)                                      00560 HEADING! = TRUEARC! * (180.0/P!!)                                       00570 RETURN                                                                  __________________________________________________________________________

What is claimed is:
 1. A method for utilizing the common database ofpresently existing Air Traffic Control (ATC) facilities which include asearch radar unit, a radio beacon unit and a common digitizer to trackaircraft and aid collision avoidance, the steps of whichcomprise:acquiring the data from the common digitizer without affectingthe transmission of data to the ATC presently existing host computer,wherein azimuth and range information is acquired for all aircraft beingtracked; creating a plot message by filtering out non-positional datafrom the common digitizer; converting polar coordinates of the plotmessage to rectangular coordinates; creating and encoding a data blockfrom the plot message containing information on all aircraft beingtracked by the ATC facility by using an auxiliary computer means;reading the data block into temporary storage; transmitting the datablock to receiving stations; receiving the data block at a receivingstation; decoding the data block; and displaying the data in humanreadable form.
 2. The method of claim 1, wherein the steps are repeatedto obtain updated information in the data block for displaying same. 3.The method of claim 1, wherein the data block is encoded by the stepsof:initializing a tracking array; updating the tracking array with theplot message; extrapolating a best fit line with the updated trackingarray data and updating the tracking array with the best fit linethereby defining a new data block which is transmitted to receivingstations.
 4. The method of claim 1, wherein the data from the commondigitizer is defined as a raw data string and wherein, in the filteringstep, the raw data string is stored at a first file (file 1) and upon anappropriate time command the data is stored a second file (file 2) andwherein, the data string from each of the files is read into thecomputer means at appropriate times.
 5. The method of claim 1, whereinthe data from the common digitizer is assigned a time signature at thefiltering step which is equal to the actual time less the time that ithas taken to process the data from the time the data entered the ATC. 6.The method of claim 5, wherein the data from the common digitizer isdefined as a raw data string and wherein, in the filtering step, the rawdata string is stored at a first file (file 1) and upon an appropriatetime command the data is stored a second file (file 2) and wherein thedata string from each of the files is read into the computer means atappropriate times depending on the time signature.
 7. The method ofclaim 1, wherein file 1 and file 2 comprise random access memory (RAM).8. The method of claim 1, wherein the ATC facility tracks discrete andnon-discretely addressable transponders.
 9. The method of claim 1,wherein the step of acquiring the data from the common digitizerincludes the steps of:sychcronizing with the signal rate of the commondigitizer; duplicating the signal from the common digitizer and allowingthe original signal to pass unaffected to the ATC host computer andsending the duplicated signal to be encoded.
 10. The method of claim 1,wherein the step of transmitting the signal includes transmitting thedata block asynchronously and having a stop bit in the block to causethe transmission to pause between the end of one block and the beginningof another.
 11. Apparatus for a ground radar and information displaysystem (GRIDS) for presently existing Air Traffic Control facilities(ATC) which include a search radar unit, a radio beacon unit and acommon digitizer, comprising:an auxiliary portion of the groundfacility, including;mean for acquiring data from the common digitizer;means for filtering out non-positional data from the common digitizerand temporarily storing the positional data; auxiliary ground computermeans for performing data conversion and encoding on the positional dataand temporarily storing the converted data in a block; and radio meansfor transmitting the encoded data block; and a display facility,including;means for receiving the encoded data block; computer means fordecoding the signal; and display means for displaying information fromthe ground station, whereby information from the ground station can bedisplayed and updated at the receiving unit without affecting any of thepresently existing facilities.
 12. Apparatus for a ground radar andinformation display system as set forth in claim 11, wherein the datablock contains complete data on all relevant aircraft.
 13. Apparatus fora ground radar and information display system as set forth in claim 11,wherein the data is acquired by connecting the common digitizer to adata stream splitter which duplicates the signal from the commondigitizer and sends the original data on its original path unaffected bythe duplication and sends the duplicated signal to the filtering means,whereby, the data acquisition by the auxiliary ground portion isinvisible to the ATC in general and in particular, is done withoutaffecting the transmission of data from the common digitizer to an ATChost computer.
 14. A ground radar and information display system as setforth in claim 13, wherein the data stream splitter is opticallyconnected to the common digitizer.
 15. Apparatus for a ground radar andinformation display system as set forth in claim 11, wherein theauxiliary computer includes a data filter and buffer which defines themeans for filtering out non-positional data from the common digitizerand temporarily storing the filtered data and a data buffer fortemporarily storing the converted data in a block.
 16. Apparatus for aground radar and information display system as set forth in claim 11,wherein the means for transmitting the data block comprises an auxiliaryomni-directional antenna.
 17. Apparatus for a ground radar andinformation display system as set forth in claim 16, wherein the antennatransmits on a plurality of channels.
 18. Apparatus for a ground radarand information display system as set forth in claim 11, wherein thereceiving station computer is connected to the mean for receiving theautomatically adjusts the receiving means to the desired channel. 19.Apparatus for a ground radar and information display system as set forthin claim 11, wherein the receiving means modulates the signal beforetransmission and the receiving station computer includes a demodulatorand buffer unit for temporary storage of the demodulated data block. 20.Apparatus for a ground radar and information display system as set forthin claim 11, wherein the receiving station includes a Mode A, Mode C orModes S transponder.
 21. Apparatus for a ground radar and informationdisplay system as set forth in claim 11, wherein the receiving stationincludes an optical disc-read only memory (ROM) having the navigationalmap of each available site connected to the receiving station computerfor superimposing the data block over the navigational map on thereceiving station display means.
 22. Apparatus for a ground radar andinformation display system as set forth in claim 11, wherein thereceiving station includes an audio warning speaker connected to thereceiving station computer to warn Mode S transponder equipped receivingstations of the close proximity of aircraft.